S = 11,000,000 as there are around 11 million in Wuhan.

I = 3500 as there were an estimated 3500 (approx) infected

R = 8200 as there were an estimated 8200 (approx) recovered.

Looks like the website with the link to the excel formula is down.

]]>I recall the 80s as a young man in my 20s. When no one was discussing the maths (no internet for geeks). But Maggie was a trained scientist and UK policy was very effective in persuading people to change their habits so that p, the transmission rate fell sharply which was good. And also γ, the total contact rate fell sharply, about which I was more equivocal.

https://en.wikipedia.org/wiki/Transmission_risks_and_rates

The effective contact rate (denoted β) in a given population for a given infectious disease is measured in effective contacts per unit time. This may be expressed as the total contact rate (the total number of contacts, effective or not, per unit time, denoted γ), multiplied by the risk of infection, given contact between an infectious and a susceptible individual. This risk is called the transmission risk and is denoted p. Thus:

β = γ X p

The total contact rate, γ, will generally be greater than the effective contact rate, β, since not all contacts result in infection. That is to say, p is almost always less than 1 and it can never be greater than 1, since it is effectively the probability of transmission occurring.

]]>Thanks for you comment – I don’t think I worded the explanation very well. If you think of beta as the average number of disease-spreading contacts made by each infected individual per day then a beta of 1.07 (per day) means on average an infected person will infect 1.07 other people each day. I might try to make that clearer in the post! Sometimes the SIR models give a value for beta by dividing by N as well (i.e in this case 1.07/11,000,000), but in the equations above the division by N is already there.

]]>β represents the contact rate – which is how likely someone will get the disease when in contact with someone who is ill.

Have I missed something – how can the contact rate be > 1 ?

It is a probability isn’t it?